Because of their excellent weathering resistance, ozone resistance and heat aging characteristics, ethylene-.alpha.-olefin-nonconjugated polyene random copolymers (sometimes referred to simply as "ethylene copolymer rubbers" hereinafter) such as an ethylene-propylene-polyene terpolymer (EPDM) have been heretofore widely used as automobile materials, electrical wire materials, building and civil engineering materials and industrial materials.
The ethylene-.alpha.-olefin-nonconjugated polyene random copolymers used for such applications are desired to have good moldability, high vulcanizing rate and high vulcanization strength.
Of the ethylene copolymer rubbers, an ethylene-propylene-ethylidenenorbornene (ENB) copolymer rubber is known as a high rate vulcanizable copolymer, but the conventionally known ethylene-propylene-ENB copolymer rubber is poor in extrusion moldability.
An ethylene-propylene-dicyclopentadiene copolymer rubber is known as a copolymer rubber of excellent extrusion moldability, but this copolymer is low in the vulcanizing rate, and its vulcanization strength is not high.
For these reasons, how desired are the advents of an ethylene-.alpha.-olefin-nonconjugated polyene random copolymer and a rubber composition which are excellent in processability, vulcanizing rate and mechanical strength such as vulcanization strength and a process for preparing said random copolymer rubber.
Under such circumstances as described above, the present inventors have earnestly studied ethylene-.alpha.-olefin-nonconjugated polyene random copolymers, rubber compositions and processes for preparing the ethylene copolymer rubbers. As a result, they have found that an ethylene-.alpha.-olefin-nonconjugated polyene random copolymer having a long-chain branch in its molecule and having such properties that (i) the copolymer contains (a) units derived from ethylene and (b) units derived from the .alpha.-olefin of 3 or more carbon atoms in a molar ratio of 40/60 to 95/5 [(a)/(b)], (ii) the iodine value is in the range of 1 to 50, (iii) the intrinsic viscosity (.eta.) is in the range of 0.1 to 8.0 dl/g, and (iv) the g.eta.*, value is in the range of 0.2 to 0.9 or the g' value is not higher than 0.9, and a vulcanizable rubber composition containing this random copolymer have the above-mentioned excellent characteristics. The present inventors have also found that this random copolymer can be efficiently prepared by the use of a catalyst containing a specific metallocene compound. Based on these findings, the present invention has been accomplished.